Referring to a printed circuit board for mounting an integrated circuit or the like, electrical characteristics are inspected to confirm that the wiring pattern of the circuit board has a predetermined performance before mounting the integrated circuit or the like.
In the electrical inspection, for example, an inspecting head is incorporated into an inspecting tester including the delivery mechanism of the circuit board and inspecting head portions are exchanged to inspect different circuit boards.
For example, as is disclosed in Patent Document 1 (Japanese Laid-Open Patent Publication No. 1994-94768), there has been proposed a method using an inspecting jig having a structure in which a metallic inspecting pin to be electrically conducted in contact with an electrode to be inspected in a circuit board to be inspected is infixed into a board.
As is disclosed in Patent Document 2 (Japanese Laid-Open Patent Publication No. 1993-159821), moreover, there has been known a method using an inspecting jig in which an inspecting head having a conductive pin, a circuit board for pitch conversion which is referred to as an off-grid adapter and an anisotropically conductive sheet are combined.
In the method using an inspecting jig to cause a metallic inspecting pin to directly come in contact with the electrode to be inspected in the circuit board to be inspected as described in the Patent Document 1 (Japanese Laid-Open Patent Publication No. 1994-94768), however, there is a possibility that the electrode of the circuit board to be inspected might be damaged due to the contact with the conductive pin formed of a metal.
In recent years, particularly, the fineness and density of a circuit in the circuit board has been increased. In the case in which such a printed circuit board is to be inspected, it is necessary to pressurize an inspecting jig at a high pressure in order to cause a large number of conductive pins to be simultaneously conducted in contact with an electrode to be inspected in a circuit board to be inspected. Consequently, the electrode to be inspected is apt to be damaged.
In an inspecting jig for inspecting the printed circuit board having the fineness and density increased, it has been technically hard to infix a large number of metallic pins into the board at a high density. Moreover, a manufacturing cost is also increased. In the case in which a part of the metallic pins are damaged, furthermore, it is hard to repair or exchange them.
On the other hand, in the inspecting jig using the anisotropically conductive sheet as described in the Patent Document 2 (Japanese Laid-Open Patent Publication No. 1993-159821), the electrode to be inspected in the circuit board to be inspected comes in contact with the electrode of the board for pitch conversion through the anisotropically conductive sheet. Therefore, there is an advantage that the electrode to be inspected in the circuit board to be inspected is damaged with difficulty. Moreover, the board for carrying out the pitch conversion is used. Therefore, the inspecting pin to be infixed into the board can be infixed at a greater pitch than the pitch of the electrode to be inspected in the circuit board to be inspected. For this reason, it is not necessary to infix the inspecting pin at a minute pitch. Consequently, there is also an advantage that the manufacturing cost of the inspecting jig can be reduced.
In the inspecting jig, however, it is necessary to create the board for pitch conversion and the inspecting jig for infixing the inspecting pin for each circuit board to be inspected which is the inspecting target. Therefore, the same number of inspecting jigs as that of the printed circuit boards which are the circuit boards to be inspected are required.
In the case in which a plurality of printed circuit boards is produced, therefore, there is a problem in that a plurality of inspecting jigs is to be retained corresponding thereto. In recent years, particularly, the manufacturing cycle of an electronic apparatus has been shortened and a reduction in the production period of a printed circuit board to be used in a product has been progressed. Consequently, the inspecting jig cannot be used for a long period of time. Thus, there is a problem in that the inspecting jig is to be produced every time the production of the printed circuit board is changed over.
For a countermeasure against such problems, for example, there has been proposed an inspecting apparatus using an inspecting jig of a so-called universal type using a relay pin unit disclosed in Patent Documents 3 to 5 (Japanese Laid-Open Patent Publication No. 1995-248350, Japanese Laid-Open Patent Publication No. 1996-271569 and Japanese Laid-Open Patent Publication No. 1996-338858).
FIG. 36 is a sectional view showing the inspecting apparatus using the inspecting jig of a universal type. The inspecting apparatus comprises a pair of first and second inspecting jigs 111a and 111b, and these inspecting jigs include circuit board side connectors 121a and 121b, relay pin units 131a and 131b, and tester side connectors 141a and 141b. 
The circuit board side connectors 121a and 121b include boards 123a and 123b for pitch conversion, and anisotropically conductive sheets 122a, 122b, 126a and 126b provided on both sides thereof.
The relay pin units 131a and 131b include a large number of conductive pins 132a and 132b (for example, 5000 pins) provided on a lattice point at a constant pitch (for example, a pitch of 2.54 mm), and a pair of insulating plates 134a and 134b for supporting the conductive pins 132a and 132b to be vertically movable.
The tester side connectors 141a and 141b include connector boards 143a and 143b for electrically connecting the testers to the conductive pins 132a and 132b when interposing the circuit board 101 to be inspected between the inspecting jigs 111a and 111b by pressure, anisotropically conductive sheets 142a and 142b provided on the sides of the conductive pins 132a and 132b of the connector boards 143a and 143b, and base plates 146a and 146b. 
When the inspecting jig using the relay pin unit is to inspect printed circuit boards which are different targets to be inspected, it is sufficient that the circuit board side connectors 121a and 121b are exchanged with members corresponding to the circuit board 101 to be inspected, and the relay pin units 131a and 131b and the tester side connectors 141a and 141b can be used in common.
The printed wiring board to be the circuit board 101 to be inspected has been multilayered and increased in a density. A variation in a height and a warpage of the board itself are actually caused by the electrodes 102 and 103 to be inspected, for example, a solder ball electrode such as a BGA in the direction of a thickness. In order to achieve an electrical connection to the electrodes 102 and 103 to be inspected which are inspecting points on the circuit board 101 to be inspected, therefore, it is necessary to pressurize the first inspecting jig 111a and the second inspecting jig 111b at a high pressure, thereby flatly deforming the circuit board 101 to be inspected, and it is necessary to cause the variation in the heights of the electrodes 102 and 103 to be inspected to follow the heights of the electrodes 102 and 103 to be inspected on the sides of the first inspecting jig 111a and the second inspecting jig 111b. 
In the conventional inspecting jig of a universal type, the heights of the electrodes 102 and 103 to be inspected are followed by a movement in the axial direction of the conductive pins 132a and 132b in order to maintain a follow-up for the same heights. However, the amount of the movement in the axial direction of the conductive pins 132a and 132b also has a restriction. For this reason, the follow-up for the heights of the electrodes 102 and 103 to be inspected is not excellent in some cases. Consequently, a defective conduction is generated so that an accurate inspection cannot be carried out.
In the inspecting jig of a universal type, moreover, a press pressure in the case in which the circuit board 101 to be inspected is interposed by pressure between the first inspecting jig 111a and the second inspecting jig 111b is absorbed into the upper and lower anisotropically conductive sheets 122a, 122b, 126a, 126b, 142a and 142b. 
In the inspecting jig of a universal type, therefore, it is necessary to arrange the conductive pins 132a and 132b at a constant interval in order to support the boards 123a and 123b for pitch conversion and to disperse the press pressure.
In the conventional inspecting jig of a universal type, moreover, the press pressure is received by the conductive pins 132a and 132b. For this reason, it is necessary to arrange a large number of conductive pins 132a and 132b at a constant interval.
In some cases in which the insulating plates 134a and 134b having at least 10000 through holes are to be formed at a pitch of 0.75 mm, for example, corresponding to the microfabrication of the electrode of the circuit board 101 to be inspected, therefore, strengths are reduced if the thicknesses of the boards of the insulating plates 134a and 134b are small and they are broken due to bending. For this reason, it is necessary to increase the thicknesses of the insulating plates 134a and 134b. 
If the through hole to be formed is fine, for example, has a diameter of approximately 0.5 mm and the insulating plates 134a and 134b have thicknesses of 5 mm or more, however, a blade of a drill is defective and broken to fail in the processing of the insulating plate in respect of a strength of the blade of the drill in many cases in which the through hole is to be formed by one drill processing.
For this reason, the drill processing is carried out to almost a half of a thickness from either surface of the insulating plate, and furthermore, is carried out in the same portion from the other surface side to form the through hole, thereby processing the insulating plate. In this case, there is a problem in that a drill processing work to be a double of the number of the through holes to be formed on the insulating plate is required and the processing step is thus complicated.
In the conventional inspecting jig of a universal type, moreover, there are used, as the anisotropically conductive sheets 122a and 122b constituting the circuit board side connectors, the anisotropically conductive sheets of an uneven distribution type which include a plurality of conductive path forming portions extended in the direction of a thickness and insulating portions for insulating these conductive path forming portions from each other and in which conductive particles are contained in only the conductive path forming portion and are distributed unevenly in a planar direction, and the conductive path forming portion is protruded toward the either surface side of the sheet. In the case in which the conductive path forming portion is deteriorated (a resistance value is increased) by a repetitive use in an inspection and the anisotropically conductive sheet is exchanged, it is necessary to align the anisotropically conductive sheet with the board for pitch conversion and to align the circuit board side connector with the relay pin unit every exchange. The aligning work is complicated to cause a reduction in an inspection efficiency.
When the electrodes in the circuit board are arranged at a minute pitch of 200 μm or less, for example, it is easy to generate the positional shift of the anisotropically conductive sheet due to a repetitive contact with a plurality of circuit boards in the case in which the circuit boards are continuously inspected by using the anisotropically conductive sheet described above. Consequently, the conductive path forming portion of the anisotropically conductive sheet and the position of the electrode in the circuit board are not coincident with each other so that an excellent electrical connection cannot be obtained. For this reason, an excessively great resistance value is measured so that a printed circuit board to be originally decided to be an excellent product is easily decided erroneously to be a defective product.
In the case in which there is obtained an anisotropically conductive elastomer sheet of an uneven distribution type for inspecting the circuit board having the electrodes to be inspected which are disposed at a small pitch in a distance of 100 μm or less between the electrodes to be inspected, moreover, it is necessary to carry out a formation in such a manner that a width of the insulating portion for mutually insulating the adjacent conductive path forming portions is equal to or smaller than 100 μm. In a conventional method of manufacturing a sheet by metal molding which has been disclosed in Patent Document 6 (Japanese Laid-Open Patent Publication No. 1991-196416), for example, it is hard to form the insulating portion having a width of 100 μm or less because of a magnetic field action with an adjacent metal mold magnetic pole. In the anisotropically conductive elastomer sheet of an uneven distribution type according to the conventional manufacturing method, therefore, a lower limit of the distance between the electrodes of the circuit board at which the inspection can be carried out is approximately 80 to 100 μm depending on a thickness of the sheet.
For this reason, it is very hard to form, by the metal molding method, the anisotropically conductive elastomer sheet of an uneven distribution type for inspecting the circuit board having the inspected electrodes disposed at a small pitch in which the distance between the inspected electrodes is equal to or smaller than 50 μm. Consequently, the anisotropically conductive elastomer sheet of an uneven distribution type has not been obtained substantially.
On the other hand, it is possible to obtain a high resolution by reducing a thickness of a so-called anisotropically conductive elastomer sheet of a dispersion type in which conductive particles are arranged in a direction of a thickness and are uniformly dispersed in a planar direction. Therefore, it is possible to inspect the circuit board in which the distance between the electrodes to be inspected is equal to or smaller than 50 μm in the resolution by setting a thickness of approximately 30 μm, for example.
In a thin anisotropically conductive elastomer sheet of a dispersion type which has a thickness of approximately 30 μm, however, the absorption of a mechanical shock generated by an elasticity of a sheet body or a capability for constituting an electrical connection to be carried out by a soft contact of electrodes which is one of characteristics of the anisotropically conductive elastomer sheet is eliminated almost completely. In the case in which a circuit board to be inspected which includes a large number of inspected electrodes having a variation in a height is connected to the inspecting apparatus, therefore, it is hard to connect a large number of inspected electrodes at the same time due to a reduction in a step absorbing capability of the anisotropically conductive elastomer sheet. For example, in a circuit board in which a large number of electrodes are formed by plating, a variation in a height of each of the electrodes is approximately 20 μm.
In the anisotropically conductive elastomer sheet of a dispersion type, a compressibility capable of stably achieving an electrical conduction is equal to or smaller than approximately 20% in a compression in a direction of a thickness. For example, when the compression is carried out beyond 20%, the electrical conduction in a transverse direction is increased so that an anisotropy of the conduction is deteriorated, and furthermore, a permanent deformation of the elastomer to be a base material is generated so that a repetitive use is hard to perform. For this reason, in the case in which the circuit board including the electrode having the variation in a height of approximately 20 μm is to be inspected, it is necessary to use the anisotropically conductive elastomer sheet of a dispersion type which has a thickness of 100 μm or more.
When the anisotropically conductive elastomer sheet of a dispersion type which has a thickness of 100 μm or more is used, however, there is a problem in that it is substantially impossible to inspect a circuit board having electrodes to be inspected which are disposed at a small pitch of 50 μm or less because of a deterioration in a resolution.
In an anisotropically conductive elastomer sheet of a dispersion type which has a small thickness, furthermore, a capability for absorbing a mechanical shock is small because of a small elasticity of a sheet body. In a use for an adaptor for inspecting a circuit board to repetitively inspect the circuit board, the anisotropically conductive elastomer sheet is deteriorated quickly. For this reason, the anisotropically conductive elastomer sheet of a dispersion type is to be exchanged often so that an exchanging work is complicated and an inspection efficiency for the circuit board is reduced.
From the foregoing, in the circuit board inspecting adaptor using the anisotropically conductive elastomer sheet which serves to inspect the circuit board having the electrodes to be inspected that are disposed at a small pitch of 50 μm or less, all of a resolution, a step absorbing power and a repetitive use durability cannot be satisfied.
In the case in which a four-terminal inspection is carried out in order to detect a latent electrical defect of the circuit board with high precision, furthermore, two inspection electrodes (for a voltage and a current) of the circuit board for an inspection are connected to one of the electrodes to be inspected in the circuit board to be inspected. For this reason, a distance between the inspection electrodes to make a pair of the circuit board for an inspection is decreased. For example, in the case in which the pitch between the electrodes to be inspected in the circuit board to be inspected is 200 μm, a diameter of the electrode to be inspected is approximately 100 μm and two inspection electrodes of the circuit board for an inspection are connected to the electrode to be inspected which has a diameter of approximately 100 μm. Therefore, the distance between the inspection electrodes of the circuit board for an inspection is approximately 30 to 40 μm.
As described above, in the conventional anisotropically conductive sheet of an uneven distribution type or anisotropically conductive sheet of a dispersion type, it is impossible to sufficiently obtain all of a resolution, a step absorbing power, a cushioning property and a durability with respect to an inspecting apparatus for inspecting a circuit board having a large number of electrodes to be inspected.    Patent Document 1: Japanese Laid-Open Patent Publication No. 1994-94768    Patent Document 2: Japanese Laid-Open Patent Publication No. 1993-159821    Patent Document 3: Japanese Laid-Open Patent Publication No. 1995-248350    Patent Document 4: Japanese Laid-Open Patent Publication No. 1996-271569    Patent Document 5: Japanese Laid-Open Patent Publication No. 1996-338858    Patent Document 6: Japanese Laid-Open Patent Publication No. 1991-196416